1. Field of the Invention
The present invention relates to a printer and a ribbon cassette used in the printer.
2. Description of the Related Art
To facilitate mounting and ink ribbon to a printer, there has been known a ribbon cassette, having two ribbon-supporting arms, that can be mounted to the printer by-merely pressing the ribbon cassette in place. The ribbon cassette eliminates the need for a user to touch the ink ribbon directly, so that he or she can replace the ink ribbon without staining his or her hands with ink. The structure and mounting method of the ink ribbon cassette will be described while referring to FIGS. 1 and 2.
The ribbon cassette 110 includes a pair of arms 115, a pair of ribbon drive rollers 112, a ribbon brake 113, and a Mobius portion 14. The arms 115 are provided at either end of the ribbon cassette 110 extending toward the sheet to be printed. The ribbon drive rollers 112 are provided in opposition at one end of the ribbon cassette 110 so as to be rotatable about respective axial shafts 112b. An ink ribbon 11 is passed between the ribbon drive rollers 112 and is driven by the ribbon drive rollers 112 in the direction indicated by an arrow in FIG. 1. The ribbon brake 113, which is for applying tension to the ribbon 11, and the Mobius portion 14, which is for reversing sides of the ribbon 11, are provided at the other end of the ribbon cassette 110.
A ribbon motor 121 and cassette holders 20 are provided on the mounting base 122 of the printer. The cassette holders 20 have a snap-fit portion 20a for maintaining the ribbon cassette 110 in place in the-printer. The ribbon motor 121 is for driving the ribbon drive rollers 112. The ribbon cassette 110 is mounted in the printer by engaging the ribbon cassette 110 in the snap-fit portion 20a. When the ribbon cassette 110 is mounted in the printer in this way, the rotation shaft of one of the ribbon drive rollers 112 is brought into alignment with the shaft of the ribbon motor 121. The lower tip of that ribbon drive roller 112 engages directly with the output shaft of the ribbon motor 121, thereby allowing transmission of drive power. The engagement between the lower tip of the ribbon drive roller 112 and the output shaft of the ribbon motor 121 is the same as engagement between a tape spool of a tape cassette and a drive shaft of a tape player. Both cases require leeway between engaging components of one millimeter or more, which results in a loose fit between engaging components.